/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.streaming.api.transformations;

import org.apache.flink.annotation.Internal;
import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.api.dag.Transformation;
import org.apache.flink.streaming.api.operators.ChainingStrategy;
import org.apache.flink.streaming.api.operators.StreamOperatorFactory;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

/**
 * Base class for transformations representing the application of a {@link
 * org.apache.flink.streaming.api.operators.MultipleInputStreamOperator} to input {@code
 * Transformations}. The result is again only one stream.
 *
 * @param <OUT> The type of the elements that result from this {@code MultipleInputTransformation}
 */
@Internal
public abstract class AbstractMultipleInputTransformation<OUT> extends PhysicalTransformation<OUT> {

    protected final List<Transformation<?>> inputs = new ArrayList<>();
    protected final StreamOperatorFactory<OUT> operatorFactory;

    public AbstractMultipleInputTransformation(
            String name,
            StreamOperatorFactory<OUT> operatorFactory,
            TypeInformation<OUT> outputType,
            int parallelism) {
        super(name, outputType, parallelism);
        this.operatorFactory = operatorFactory;
    }

    @Override
    public List<Transformation<?>> getInputs() {
        return inputs;
    }

    /** Returns the {@code TypeInformation} for the elements from the inputs. */
    public List<TypeInformation<?>> getInputTypes() {
        return inputs.stream().map(Transformation::getOutputType).collect(Collectors.toList());
    }

    /** Returns the {@code StreamOperatorFactory} of this Transformation. */
    public StreamOperatorFactory<OUT> getOperatorFactory() {
        return operatorFactory;
    }

    @Override
    public List<Transformation<?>> getTransitivePredecessors() {
        return inputs.stream()
                .flatMap(input -> input.getTransitivePredecessors().stream())
                .collect(Collectors.toList());
    }

    @Override
    public final void setChainingStrategy(ChainingStrategy strategy) {
        operatorFactory.setChainingStrategy(strategy);
    }
}
